A seat apparatus for a vehicle is disclosed in, for example, JP2008-134232A. According to JP2008-134232A, a plurality of load detecting devices is arranged between a seat-side fixing member and a pair of upper rails that is slidable relative to a vehicle floor in a front-rear direction of the vehicle. More specifically, four load detecting devices are respectively arranged at front ends and rear ends of the pair of upper rails that are arranged to face each other in a left-right direction of the vehicle.
On the other hand, a device for measuring a weight of a seat is disclosed in JP2001-150997A, in which the number of load detecting devices is reduced in order to reduce a cost of manufacturing, assembling and wiring. According to JP2001-150997A, two load detecting devices are respectively arranged between a seat-side fixing member and rear ends of a pair of upper rails. Front ends of the pair of upper rails are respectively spot-fixed or pivotally connected to the seat-side fixing member. Thus, the number of load detecting devices is reduced.
According to configurations disclosed in JP2001-150997A, however, depending on an orientation of a vehicle driven downhill and on a posture and a seating position of an occupant, a load of the occupant, seated on the seat, may not be accurately detected. When the vehicle is driven downhill, a center of gravity of the occupant, seated on the seat, is positioned at a more forward side of the vehicle than a position of the center of gravity of the occupant while the vehicle is driven on a leveled road. Because the load detecting devices according to JP2001-150997A are arranged only at a rear end of the vehicle, a load received by the load detecting devices may be decreased. Further, a center of gravity of the occupant, seated at a front portion of the seat, is positioned at a more forward side of the vehicle than a position of the center of the gravity of the occupant, seated at a rear portion of the seat. In such a case also, a load received by the load detecting devices may be decreased.
A need thus exists for a seat apparatus for a vehicle, which is not susceptible to the drawback mentioned above.